P7142-AG impacts on endothelial cell activation and endothelial cell viability in vitro and impairs endothelial repair in vivo

Background

The endocannabinoid (eCB) 2-arachidonoylglycerol (2-AG) is a known modulator of inflammation and few studies have addressed its influence on myeloid cells in the context of atherogenesis. However, the impact of 2-AG on endothelial cell function has not been studied before.

Methods

Endothelial repair was studied in two treatment groups of wildtype mice following electrical denudation of the common carotid artery at a length of 3000 μm. One group received the monoacylglycerol lipase (MAGL)-inhibitor JZL184 [5 mg/kg i.p.], which impairs 2-AG degradation and thus causes elevated 2-AG levels, the other group received vehicle. The residual endothelial gap at five days in either group was visualized by Evan's blue staining. In vitro, the effect of 2-AG on human coronary artery endothelial cell (HCAEC) viability was assessed by an XTT-based assay. Endothelial activation was studied by an adhesion assay of THP-1 monocytes to 2-AG-preconditioned HCAEC. HCAEC migration, ROS-production, expression of NADPH oxidases, and secretion of inflammatory cytokines were assessed by Boyden chamber, qPCR, and colorimetric assays.

Results

Treatment with JZL184 produced a significant increase in 2-AG levels and impaired reendothelialisation in wildtype mice following electrical injury of the common carotid artery. The residual denudation at 5 days yielded 2291±286 μm in JZL184-treated animals vs. 1505±223 μm in vehicle treated controls (n=18–19; p<0.05). In vitro, JZL184 significantly reduced viability of HCAEC at 24 hours (0.31±0.10 vs. 1.00±0.08; n=3; p<0.01). Finally, 2-AG promoted HCAEC activation resulting in a significant increase in THP-1 monocyte adhesion to HCAEC following pre-treatment of HCAEC with 2-AG (0.17±0.03 THP-1 cells per HCAEC vs. 0.07±0.01 THP-1 cells per HCAEC; n=3; p<0.05). Besides, HCAEC migration, ROS-production, expression of NADPH oxidases and secretion of inflammatory cytokines were unaffected by 2-AG.

Conclusion

Elevated 2-AG levels appear to hamper endothelial repair and to promote HCAEC activation and cell death. Our data suggest that besides its influence on myeloid cells, 2-AG is also adverse to endothelial integrity which might promote early atherosclerotic lesion formation. Thus, decreasing vascular 2-AG levels might represent a promising therapeutic strategy for the prevention of atherosclerosis and coronary heart disease.

P4140Myeloid but not endothelial expression of the CB2 receptor promotes atherogenesis in the context of elevated levels of the endocannabinoid 2-arachidonoylglycerol

Background

The endocannabinoid 2-arachidonoylglycerol (2-AG) is an inflammatory mediator and ligand to the cannabinoid receptors CB1 and CB2, which are expressed on myeloid and endothelial cells. 2-AG has recently been described to promote atherogenesis in ApoE-deficient mice. While the CB2 receptor has previously been considered to solely exert anti-inflammatory and atheroprotective effects, newer data have raised the notion, that CB2 might exert atherogenic effects in the context of elevated 2-AG plasma levels. In the present study, we investigated the atherogenic mechanisms of 2-AG and the role of the CB2 receptor on myeloid and endothelial cells in atherogenesis using cell-specific knockout mouse models.

Methods

Two mouse models with atherogenic background and distinct cell-specific knockouts of the CB2 receptor on myeloid (ApoE−/−LysMcreCB2fl/fl) or endothelial cells (ApoE−/−Tie2creCB2fl/fl) were created. Mice were treated with JZL184, which inhibits 2-AG-degrading enzyme monoacylglycerol lipase, and thereby elevates 2-AG plasma levels, or with vehicle (DMSO), while being fed a high-fat diet for four weeks. Plaque volume and plaque composition were analyzed. In vitro, macrophages were treated with 2-AG and mRNA levels of adhesion molecules, scavenger receptors and chemokines, the production of reactive oxygen species (ROS) and the release of myeloperoxidase (MPO) were determined using qPCR, fluorometric assays and ELISA respectively.

Results

Elevated levels of 2-AG promote atherogenesis in ApoE-deficient mice (JZL184 vs. DMSO: 39.6±2.1% vs. 32.6±2.4%; n=14; p<0.05). The atherogenic effect of 2-AG is abrogated in mice lacking myeloid CB2 receptor expression (35.0±2.0% vs. 34.0±2.5%; n=14–16; p>0.05) but not in mice lacking endothelial CB2 receptor expression (37.1±3.1% vs. 20.9±2.6%; n=10–12; p<0.01). In vitro, 2-AG significantly increases transcription of adhesion molecule ICAM-1 (2.09±0.42 –fold; n=5–6; p<0.05), chemokine receptor CCR-1 (2.04±0.46 -fold; n=10–11; p<0.05) and scavenger receptor CD36 (8.02±1.89-fold; n=3; p<0.05) in 2-AG-treated macrophages. These effects are mitigated by pharmacological inhibition of CB2. Furthermore, 2-AG significantly increases myeloperoxidase (MPO) release in monocytes in a CB receptor-dependent fashion (451±23 pg/ml vs. 151±8.3 pg/ml; n=3–4; p<0.01) and promotes ROS production (2698±24 pdu vs. 1981±27 pdu; n=8; p<0.01).

Conclusion

Elevated 2-AG levels show an atherogenic effect in vivo which is dependent on the presence of the CB2 receptor on myeloid cells. Our in vitro data reveal 2-AG to promote pro-inflammatory signaling in macrophages and elucidate a previously unrecognized link between the endocannabinoid system and MPO in monocytes. In summary, cell-specific effects of the endocannabinoid system will have to be taken into account to facilitate its exploitation as an anti-atherosclerotic drug target.

Acknowledgement/Funding

This work was supported by the Bonfor program of the University of Bonn [grant number O-109.0057 to JJ].

[Bilateral 23Na MR imaging of the breast and quantification of sodium concentration]

A novel setup for (23)Na MRI, which allows bilateral imaging of the breast, is presented. For this purpose a figure-eight receive-only (23)Na surface coil was developed. For our experiments on three samples with NaCl solutions of different sodium concentrations and two female subjects we used an asymmetric birdcage coil in transmit mode and the developed surface coil for receiving the signal at 3T. Imaging of the samples showed the applicability of the employed normalization method for measuring the distribution of sodium concentration. In a sample of concentration [Na(+)]=51mM we achieved SNR=70 at a nominal isotropic resolution of 2,5mm (TR=66ms, TE=0,6ms, TA=20min). Furthermore we showed that by means of this setup it is possible to quantify the sodium concentration in breast tissue (TSC) of a female subject with an accuracy of 23% (TR=150ms, TE=0,5ms, TA=45min).